Recently, switching power supply apparatuses are developed toward miniaturization or high power density. Generally, the switching power supply apparatus comprises a magnetic assembly (e.g., an inductor or a transformer). The volume, weight, loss and cost of the magnetic assembly are very critical to the switching power supply apparatus. As known, the increase of switching frequency of the switching power supply apparatus can reduce the volume of the magnetic assembly and increase the power density of the switching power supply apparatus. As the frequency of the switching power supply apparatus is increased, the requirement of designing the magnetic assembly becomes more stringent. In the high-frequency application, it is important to reduce the loss of the magnetic assembly without increasing the overall volume.
Generally, the loss of the magnetic assembly contains core loss and winding loss. In the high-frequency application, the reduction of the eddy-current loss is effective to reduce the winding loss of the magnetic assembly. In the high-frequency application of the magnetic assembly, a Litz wire or a foil conductor is used in the winding assembly of the magnetic assembly. As known, the winding assembly with the Litz wire has reduced eddy-current loss. However, since each strand of the Litz winding is covered with an insulation layer and the Litz wire comprises many strands, the Litz winding has a small filling factor and the heat generated by the Litz wire is difficultly dissipated. Moreover, in comparison with the foil winding assembly, the Litz winding assembly is detrimental to the flat design and mass production. Consequently, the Litz winding assembly is gradually replaced by the foil winding assembly. In other words, while designing the magnetic assembly, it is important to reduce the winding loss of the foil winding assembly.
Conventionally, a magnetic assembly (e.g., a planar inductor) comprises a magnetic core, a foil winding assembly and a low-permeability structure. The magnetic core is constituted by plural magnetic legs. The low-permeability structure is formed in one of the plural magnetic legs in order to prevent the occurrence of magnetic saturation. The foil winding assembly comprises plural layers of winding parts.
The parameters influencing the winding loss of the magnetic assembly include the conductor thicknesses of the winding parts. Conventionally, for easily designing and producing the winding assembly, all conductor layers of the winding parts of the winding assembly have equal thickness. However, it is not an optimized option for the magnetic assembly, and the total winding loss of the magnetic assembly with this foil winding assembly is still very high.
Therefore, there is a need of provides a magnetic assembly with an optimized foil winding assembly in order to reduce the winding loss.